Weightbearing after combined medial and lateral plate fixation of AO/OTA 41-C2 bicondylar tibial plateau fractures: a biomechanical study.

BACKGROUND: Combined medial and lateral plate fixation is recommended for complex tibial plateau fractures with medial fragments or no cortical bone contact. Although such fixation is adequate to resist forces during range of motion, it may be insufficient to support immediate postoperative weightbearing. Here, we analyzed displacement, stiffness, and fixation failure during simulated full weightbearing of bicondylar tibial plateau fractures treated with combined medial and lateral locking plate fixation. METHODS: We used 10 fresh-frozen adult human cadaveric tibias and mated femurs. Osteotomies were performed with an oscillating saw and cutting template to simulate an AO Foundation and Orthopaedic Trauma Association (AO/OTA) 41-C2 fracture (simple articular, multifragmentary metaphyseal fracture). Specimens were anatomically reduced and stabilized with combined medial and lateral locking plates (AxSOS, Stryker, Mahwah, NJ). Specimens were loaded axially to simulate 4 weeks of walking in a person weighing 70 kg. The specimens were cyclically loaded from 200 N to a maximum of 2800 N. Then, if no failure, loading continued for 200,000 cycles. We measured displacement of each bone fragment and defined fixation failure as ≥5 mm of displacement. Construct stiffness and load at failure were calculated. Categorical and continuous data were analyzed using Chi-squared and unpaired t-tests, respectively. RESULTS: Mean total displacement values after 10,000 loading cycles were as follows: lateral, 0.4 ± 0.8 mm; proximal medial, 0.3 ± 0.7 mm; distal medial, 0.3 ± 0.6 mm; and central 0.4 ± 0.5 mm. Mean stiffness of the construct was 562 ± 164 N/mm. Fixation failure occurred in 6 of 10 specimens that reached 5 mm of plastic deformation before test completion. In the failure group, the mean load at failure was 2467 ± 532 N, and the mean number of cycles before failure was 53,155. After test completion, the greatest displacement was found at the distal medial fracture site (2.3 ± 1.4 mm) and lateral fracture site (2.2 ± 1.7 mm). CONCLUSIONS: Although combined medial and lateral plate fixation of complex tibial plateau fractures provides adequate stability to allow early range of motion, immediate full weightbearing is not recommended.

Comparison of Lag Versus Nonlag Screw Fixation for Long Oblique Proximal Phalanx Fractures: A Biomechanical Study.

PURPOSE: To compare lag versus nonlag screw fixation for long oblique proximal phalanx (P1) fractures in a cadaveric model of finger motion via the flexor and extensor tendons. METHODS: We simulated long oblique P1 fractures with a 45° oblique cut in the index, middle, and ring fingers of 4 matched pairs of cadaveric hands for a total of 24 simulated fractures. Fractures were stabilized using 1 of 3 techniques: two 1.5-mm fully threaded bicortical screws using a lag technique, two 1.5-mm fully threaded bicortical nonlag screws, or 2 crossed 1.14-mm K-wires as a separate control. The fixation method was randomized for each of the 3 fractures per matched-pair hand, with each fixation being used in each hand and 8 total P1 fractures per fixation group. Hands were mounted to a custom frame where a computer-controlled, motor-driven, linear actuator powered movement of the flexor and extensor tendons. All fingers underwent 2,000 full flexion and extension cycles. Maximum interfragmentary displacement was continuously measured using a differential variable reluctance transducer. Our primary outcome was the difference in the mean P1 fragment displacement between lag and nonlag screw fixation at 2,000 cycles. RESULTS: The observed differences in mean displacement between lag and nonlag screw fixation were not statistically significant throughout all time points. A two one-sided test procedure for paired samples confirmed statistical equivalence in the fragment displacement between these fixation methods at all time points, including the primary end point of 2,000 cycles. CONCLUSIONS: Nonlag screws provided equivalent biomechanical stability to lag screws for simulated long oblique P1 fractures during cyclic testing in this cadaveric model. CLINICAL RELEVANCE: Fixation of long oblique P1 fractures with nonlag screws has the potential to simplify treatment without sacrificing fracture stability during immediate postoperative range of motion.

Dermal allograft superior capsule reconstruction biomechanics and kinematics.

PURPOSE: To investigate the effect of a dermal allograft superior capsule reconstruction (SCR) on kinematics and joint pressure biomechanics immediately after simulated superior irreparable rotator cuff tear. METHODS: This controlled laboratory study tested 8 fresh-frozen cadaveric shoulders using a custom test frame. Balanced loading configuration centered the humeral head on the glenoid, and unbalanced load created a force pulling the head toward the acromion. Experimental conditions included the intact rotator cuff, irreparable supraspinatus tear (ISST), and dermal allograft SCR. A digital sensor measured glenohumeral and subacromial contact pressure maps, and a microscribe measured the acromion-humeral distance. RESULTS: Glenohumeral contact pressure of ISST was 175% (295 ± 44 kPa; P = .018) of the intact rotator cuff value (169 ± 10 kPa) at 0° in the balanced condition and 176% (P = .048) of intact at 30°. SCR decreased glenohumeral contact pressure to 110% (185 ± 27 kPa; P = .044) of intact at 0° and to 95% (P = .034) at 30°. Unbalanced ISST contact pressure was 146% (365 ± 23 kPa; P = .009) of intact (250 ± 24 kPa) at 0° and 122% (P = .045) at 60°. SCR decreased contact pressures to 110% (274 ± 21 kPa; P = .039) of intact at 0° and to 89% (P = .003) at 60°. ISST increased superior migration of the humeral head, decreasing the acromion-humeral distance by 3.0 ± 0.6 mm (P = .006) in the unbalanced condition at 0°. SCR increased the acromion-humeral distance to a value similar to that of the intact cuff (P = .003). SCR significantly lowered subacromial pressures in the unbalanced condition. CONCLUSIONS: In an irreparable supraspinatus tear model, the dermal allograft SCR showed competency in stabilizing the glenohumeral joint, decreasing glenohumeral and subacromial contact pressures, and increasing the acromion-humeral distance.

Biomechanical Analysis of Zone 2 Flexor Tendon Repair With a Coupler Device Versus Locking Cruciate Core Suture.

PURPOSE: To compare flexor tendon repair strength and speed between a tendon coupler and a standard-core suture in a cadaver model. METHODS: In 5 matched-pair fresh cadaver hands, we cut the flexor digitorum profundus tendon of each finger in zone 2 and assigned 20 tendons to both the coupler and the suture groups. Coupler repair was with low-profile stainless steel staple plates in each tendon stump, bridged by polyethylene thread. Suture repair was performed using an 8-strand locking-cruciate technique with 4-0 looped, multifilament, polyamide suture. One surgeon with the Subspecialty Certificate in Surgery of the Hand performed all repairs. Via a load generator, each flexor digitorum profundus was loaded at 5 to 10 N and cycled through flexion just short of tip-to-palm and full extension at 0.2 Hz for 2,000 cycles to simulate 6 weeks of rehabilitation. We recorded repair gapping at predetermined cycle intervals. Our primary outcome was repair gapping at 2,000 cycles. Tendons that had not catastrophically failed by 2,000 cycles were loaded to failure on a servohydraulic frame at 1 mm/s. RESULTS: Tendon repair gapping was similar between coupled and sutured tendons at 2,000 cycles. Tendons repaired with the coupler had higher residual load to failure than sutured tendons. Mean coupler repair time was 4 times faster than suture repair. CONCLUSIONS: Zone 2 flexor repair with a coupler withstood simulated early active motion in fresh cadavers. Residual load to failure and repair speed were better with the coupler. CLINICAL RELEVANCE: This tendon coupler may eventually be an option for strong, reproducible, rapid flexor tendon repair.

Synthetic coracoclavicular ligament vs. coracoclavicular suspensory construct for treatment of acromioclavicular dislocation: a biomechanical study.

BACKGROUND: A synthetic ligament (LockDown, Worcestershire, England) has become available to treat complete acromioclavicular dislocation with promising clinical results and potential benefit to avoid postoperative loss of reduction. We investigated the biomechanics of this synthetic ligament in a simulated immediate postoperative rehabilitation setting, hypothesizing that the synthetic ligament would demonstrate less superior coracoclavicular displacement to cyclic loading and higher ultimate load-to-failure values than a coracoclavicular suspensory construct. METHODS: Seven matched-pair cadaveric shoulders (mean age at time of death, 79 years) were loaded cyclically and to failure. One specimen in each pair was randomly assigned to the synthetic ligament or coracoclavicular suspensory construct. Superiorly directed 70-N cyclic loading for 3000 cycles at 1.0 Hz was applied through the clavicle in a fixed scapula simulating physiologic states during immediate postoperative rehabilitation, followed by a load-to-failure test at 120 mm/min. RESULTS: After 3000 cycles, the superior displacement of the clavicle in the synthetic ligament (9.2 ± 1.1 mm) was 225% greater than in the coracoclavicular suspensory construct (2.8 ± 0.4 mm, 95% confidence interval [CI] 3.4, 8.3; P < .001). Average stiffness of the synthetic ligament (32.8 N/mm) was 60% lower than that of the coracoclavicular suspensory construct (81.9 N/mm, 95% CI 43.3, 54.9; P < .001). Ultimate load-to-failure of the synthetic ligament was 23% (95% CI 37.9, 301.5; P = .016) lower than the coracoclavicular suspensory construct (580.5 ± 85.1 N and 750.2 ± 135.5 N, respectively). CONCLUSION: In a simulated immediate postoperative cadaveric model, the synthetic ligament demonstrated poorer biomechanics than the coracoclavicular suspensory construct. These findings suggest that a coracoclavicular suspensory construct may be preferable to a synthetic ligament if early rehabilitation is intended.

The Relationship Between Hemihamate Graft Size and Proximal Interphalangeal Joint Flexion for Reconstruction of Fracture-Dislocations: A Biomechanical Study.

PURPOSE: The purpose of this study was to determine the relationship between hemihamate graft size and proximal interphalangeal (PIP) joint flexion in a biomechanical fracture-dislocation model. METHODS: We simulated middle finger PIP fracture-dislocations in 5 cadaver hands by resecting 50% of the palmar articular surface of the middle phalanx (P2) base. Fluoroscopy was used to confirm dorsal subluxation of the middle phalanx base after resection. A 10-mm osteochondral hamate graft was contoured to reconstruct the volar lip of the middle phalanx and was progressively downsized by 2-mm increments for each trial. A computer-controlled articulator and jig simulated active flexion and extension of the fingers. Maximum PIP flexion was measured at each graft size using fluoroscopy and digital imaging software. Clinically significant flexion block was defined as PIP flexion less than 90°. RESULTS: The actual mean size of the volar defect created was 52% (3.5 mm) of the middle phalanx articular surface, which created instability and dorsal subluxation in all tested fingers. After hemihamate reconstruction, all specimens were stable throughout flexion and extension for all graft sizes. A flexion block of 90° occurred at a mean graft size of 191% of the defect (6.5 mm). With regard to the volar lip of the P2, grafts that projected an average 0.8 mm past the native volar lip position had 98° (range, 84°-107°) maximum PIP flexion. Grafts that projected an average of 3.1 mm past the native volar lip position had 90° (range, 69°-100°) maximum PIP flexion. Linear regression modeling incorporating all of the results predicted flexion block to occur at a graft size as small as 166% of the 50% volar P2 defect. In this model, for every 50% (1.7-mm) increase in graft size relative to the defect, PIP flexion decreased by approximately 6°. CONCLUSIONS: Nonanatomical hemihamate grafts produce a PIP flexion block at extreme sizes, predicted to occur at greater than 166% of a 50% P2 base articular defect in our model. This suggests that relatively large grafts can be used for reconstruction of PIP fracture-dislocations without substantial biomechanical block to PIP flexion. We suggest sizing no larger than 3 mm past the native P2 volar lip position to avoid an important mechanical block to PIP flexion. CLINICAL RELEVANCE: The information from this study helps surgeons understand how large a hemihamate graft can be used for P2 volar base reconstruction before having a negative impact on PIP flexion.

Generating Differential Ligamentotaxis Across the Radiocarpal Joint.

This study sought to determine if traction through the index or long finger metacarpal provided a selective distraction force through either the distal radius' radial or ulnar column. In eight specimens, the radius was cut transversely 1 cm proximal to the Lister tubercle. Index and long finger metacarpals were cut and two-hole plates were fixed to metacarpals. Traction forces were alternately applied to index, then long finger metacarpals, sequentially through each metacarpal from 4.5N to 89N. Traction loading through the index finger metacarpal resulted in significantly more distraction force transmitted through the distal radius fragment's radial column at all force intervals. Traction loading through long finger metacarpal resulted in significantly higher force transmission through distal radius' ulnar column. In both cohorts, force transmission increased linearly in response to higher loads. Selective traction force of either the index or long finger metacarpal resulted in differential tensioning of the distal radius' ulnar and radial columns. (Journal of Surgical Orthopaedic Advances 28(2):104-107, 2019).

Distal triceps transosseous cruciate versus suture anchor repair using equal constructs: a biomechanical comparison.

BACKGROUND/HYPOTHESIS: Suture anchor-based repair has been advocated for repair of distal triceps avulsion, but previous models have used an unequal number of sutures across the repair site. We hypothesized that there would be no difference in triceps tendon displacement between gold standard repair with transosseous cruciate bone tunnels and suture anchor repair with an equal number of sutures in the constructs. METHODS: The triceps tendon footprint was measured in 20 cadaveric elbows (10 matched pairs), and a distal triceps tendon rupture was created. The specimens in each pair were randomly assigned to transosseous cruciate repair or knotless, double-row, anatomic footprint, suture anchor repair. Specimens underwent cyclic loading to 1500 cycles and then load to failure. Footprint uncoverage was measured at 1500 cycles. Data for medial and lateral triceps tendon displacement, footprint uncoverage, and failure load were obtained. RESULTS: Triceps displacement did not differ significantly between the transosseous cruciate and the suture anchor repair group at 1500 cycles on the medial (3.6 ± 0.9 mm vs. 4.3 ± 1.6 mm [mean ± standard deviation], respectively; P = .27) and lateral side (3.1 ± 1.2 mm vs. 2.0 ± 1.2 mm, respectively; P = .06). No other differences were found between the constructs. DISCUSSION/CONCLUSION: Transosseous cruciate distal triceps repair and knotless double-row suture anchor repair using constructs with an equal number of sutures showed no significant difference in tendon displacement at 1500 loading cycles. These findings suggest that the biomechanical strength of an all-suture construct is not different from that of suture anchors for repair of distal triceps avulsions.

Is Dual Semitendinosus Allograft Stronger Than Turndown for Achilles Tendon Reconstruction? An In Vitro Analysis.

BACKGROUND: Large Achilles tendon defects pose a treatment challenge. The standard treatment with a turndown flap requires a large extensile incision, puts the sural nerve at risk, and demands slow, careful rehabilitation. Dual allograft semitendinosus reconstruction is a new clinical alternative that has the theoretical advantages of a smaller incision, less dissection, and a stronger construct that may allow for faster rehabilitation. QUESTIONS/PURPOSES: In a cadaver biomechanical model, we compared the dual allograft semitendinosus reconstruction with the myofascial turndown in terms of (1) mechanical strength and resistance to deformation and (2) failure mechanisms in reconstruction of large segmental Achilles defects. METHODS: An 8-cm segmental Achilles defect was created in 18 cadaveric lower extremities, nine matched pairs without defect or previous surgery (mean age, 78.4 years; range, 60-97 years; three female and six male pairs). Femoral neck densitometry to determine bone mineral density found that all specimens except two were osteopenic or osteoporotic. Specimens in each pair were assigned to allograft or turndown reconstruction. The constructs were mounted on a load frame and differential variable reluctance transducers were applied to measure deformation. Specimens were preconditioned and then loaded axially. Tensile force and proximal and distal construct deformation were measured at clinical failure, defined as 10 mm of displacement, and at ultimate failure, defined as failure of the reconstruction. Failure mechanism was recorded. RESULTS: Tensile strength at time zero was higher in the allograft versus the turndown construct at clinical failure (156.9 ± 29.7 N versus 107.2 ± 20.0 N, respectively; mean difference, -49.7 N; 95% CI, -66.3 to -33.0 N; p < 0.001) and at ultimate failure (290.9 ± 83.2 N versus 140.7 ± 43.5 N, respectively; mean difference, -150.2 N; 95% CI, -202.9 to -97.6 N; p < 0.001). Distal construct deformation was lower in the turndown versus the allograft construct at clinical failure (1.6 ± 1.0 mm versus 4.7 ± 0.7 mm medially and 2.2 ± 1.0 mm versus 4.8 ± 1.1 mm laterally; p < 0.001). Semitendinosus allograft failure occurred via calcaneal bone bridge fracture in eight of nine specimens. All myofascial turndowns failed via suture pullout through the fascial tissue at its insertion. CONCLUSION: In this comparative biomechanical study, dual semitendinosus allograft reconstruction showed greater tensile strength and construct deformation compared with myofascial turndown in a cadaveric model of large Achilles tendon defects. CLINICAL RELEVANCE: Further study of dual semitendinosus allograft for treatment of severe Achilles tendon defects with cyclic loading and investigation of clinical results will better elucidate the clinical utility and indications for this technique.

Fixation of Regan-Morrey Type II Coronoid Fractures: A Comparison of Screws and Suture Lasso Technique for Resistance to Displacement.

PURPOSE: The aim of this study was to compare the load to failure and stiffness achieved in coronoid fractures treated with a posterior-to-anterior screw versus a suture lasso technique. METHODS: We performed a biomechanical study using 10 pairs of fresh-frozen cadaveric elbows. A transverse osteotomy at the midpoint of the coronoid height was created to simulate a Regan-Morrey type II coronoid fracture. The specimens were randomized to screw fixation or suture lasso fixation. The load to failure and stiffness were then measured using a materials testing machine. RESULTS: Screw fixation provided greater strength and stiffness than suture lasso fixation. Mean load to failure was 405 N in the screw fixation group compared with a load to failure of 207 N for suture fixation. Screw fixation resulted in a mean stiffness of 284 kPa/mm compared with 119 kPa/mm after suture fixation. CONCLUSIONS: Screw fixation was biomechanically superior to fixation using a suture lasso technique. For coronoid fractures in which screw or suture fixation is feasible, screw fixation may provide greater resistance to displacement of the coronoid compared with a suture lasso technique. CLINICAL RELEVANCE: Clinical studies have reported a higher rate of failure after screw fixation compared with suture lasso fixation; however, this study demonstrated a greater stiffness and load to failure after screw fixation of type II coronoid fractures. Screw fixation may provide a stronger fixation construct for fractures of adequate size to support a screw. Further studies may be warranted to assess the importance of securing the anterior capsule to the coronoid tip when using a suture lasso construct because this may affect the stability of the elbow after fixation.

Comparison of Suture-Based Anchors and Traditional Bioabsorbable Anchors in Foot and Ankle Surgery.

We compared the pullout strength of a suture-based anchor versus a bioabsorbable anchor in the distal fibula and calcaneus and evaluated the relationship between bone mineral density and peak load to failure. Eight paired cadaveric specimens underwent a modified Broström procedure and Achilles tendon reattachment. The fibula and calcaneus in the paired specimens received either a suture-based anchor or a bioabsorbable suture anchor. The fibular and calcaneal specimens were loaded to failure, defined as a substantial decrease in the applied load or pullout from the bone. In the fibula, the peak load to failure was significantly greater with the suture-based versus the bioabsorbable anchors (133.3 ± 41.8 N versus 76.8 ± 35.3 N; p = .002). No significant difference in load with 5 mm of displacement was found between the 2 groups. In the calcaneus, no difference in the peak load to failure was found between the 2 groups, and the peak load to failure with 5 mm of displacement was significantly lower with the suture-based than with the bioabsorbable anchors (52.2 ± 9.8 N versus 75.9 ± 12.4 N; p = .003). Bone mineral density and peak load to failure were significantly correlated in the fibula with the suture-based anchor. An innovative suture-based anchor had a greater peak load to failure compared with a bioabsorbable anchor in the fibula. In the calcaneus, the load at 5 mm of displacement was significantly lower in the suture-based than in the bioabsorbable group. The correlation findings might indicate the need for a cortical bone shelf with the suture-based anchor. Suture-based anchors could be a viable alternative to bioabsorbable anchors for certain foot and ankle procedures.

Hook Plate Versus Suture Anchor Fixation for Thumb Ulnar Collateral Ligament Fracture-Avulsions: A Cadaver Study.

PURPOSE: To compare the biomechanical properties of hook plate fixation and suture anchor fixation for collateral ligament fracture-avulsions of the thumb metacarpophalangeal ulnar collateral ligament (UCL). METHODS: A thumb UCL fracture-avulsion model was created in 7 matched pairs of cadaver hands. An osteotomy was made parallel to the shaft of the proximal phalanx along the entire insertion of the UCL. The simulated fracture was secured using either a suture anchor tied over bone tunnels in the avulsion fragment or with a hook plate. Specimens were mounted on a servohydraulic load frame and loaded to failure. Motion perpendicular to the osteotomy was measured using an implanted 3-mm differential variable reluctance transducer device. Differences in load to failure and construct stiffness were compared and analyzed using a t test. RESULTS: The hook plate construct failed at significantly higher loads than suture fixation. Mean load to failure in the hook plate construct was 58 N (± 20 N) compared with 27 N (± 19 N) in the suture anchor construct. The difference in construct stiffness was 49 N/mm (± 17 N/mm) for the plate compared with 7 N/mm (± 13 N/mm) for the suture anchor. The main mechanism of failure for the hook plate construct was screw pullout or screw bending. The usual mechanism of failure for the suture anchor construct was anchor pullout. CONCLUSIONS: The hook plate construct was biomechanically superior to the suture anchor construct for fixation of thumb metacarpophalangeal joint UCL fracture-avulsions with regard to load to failure. CLINICAL RELEVANCE: The hook plate construct provides stronger fixation than a suture anchor for thumb UCL fracture-avulsions.

Changes in Wrist Motion After Simulated Scapholunate Arthrodesis: A Cadaveric Study.

PURPOSE: A high incidence of nonunion and relatively poor outcomes with prior fixation techniques has precluded scapholunate (SL) arthrodesis as a standard treatment for SL instability. Our purpose was to determine the impact on range of motion (ROM) of simulated SL arthrodesis via headless screw fixation. METHODS: We performed baseline wrist ROM for 10 cadaveric wrists using a standardized mounting-and-weights system. Extension, flexion, radial deviation, ulnar deviation, dart-thrower's extension, and dart-thrower's flexion were assessed. Two 3.0-mm headless compression screws were inserted across the SL joint to simulate SL arthrodesis. Goniometric measurements and fluoroscopic imaging were repeated to assess ROM differences after simulated SL arthrodesis. We assessed SL angle and gap during testing to ensure there was no significant motion between the scaphoid and lunate, thus confirming stable simulated fusion. Differences in ROM were compared between baseline and simulated SL arthrodesis using paired t tests. RESULTS: Mean SL angle remained constant between pre- and post-arthrodesis imaging (47° ± 6° vs 46° ± 4°) and did not change during post-arthrodesis ROM testing, indicating a stable simulated fusion. Compared with baseline, SL arthrodesis had a statistically significant reduction in maximum flexion of 6° and 9° based on fluoroscopy and goniometry, respectively, in dart-thrower's extension of 5° and 9° based on fluoroscopy and goniometry, respectively, and in dart-thrower's flexion of 6° for both fluoroscopy and goniometry. No other ROMs after simulated SL arthrodesis were significantly different compared with baseline. CONCLUSIONS: The effects of simulated SL arthrodesis on radiocarpal and midcarpal motion compare favorably with motion after SL soft tissue repair and other reconstructive techniques that have been previously reported. The statistically significant decreases in wrist flexion and dart-thrower's extension-flexion after simulated SL arthrodesis are of questionable clinical importance. CLINICAL RELEVANCE: These results may support reconsidering SL arthrodesis as a viable treatment option for acute or chronic SL instability with regard to apparent minimal adverse effects on functional wrist ROM.

Biomechanical characteristics of hemi-hamate reconstruction versus volar plate arthroplasty in the treatment of dorsal fracture dislocations of the proximal interphalangeal joint.

PURPOSE: To compare stability and range of motion after hemi-hamate reconstruction versus volar plate arthroplasty in a biomechanical proximal interphalangeal (PIP) joint fracture-dislocation model. METHODS: Eighteen digits from 6 cadaver hands were tested. We created defects of 40%, 60%, and 80% in the palmar base of each digit's middle phalanx, simulating an acute PIP joint fracture-dislocation. Each defect scenario was reconstructed with a hemi-hamate arthroplasty followed by a volar plate arthroplasty. A computer-controlled mechanism was used to bring each digit's PIP joint from full extension to full flexion via the digital tendons in each testing state, and in the intact state. During each testing scenario we collected PIP joint cinedata in a true lateral projection using mini-fluoroscopy. A digital radiography program was used to measure the amount of middle phalanx dorsal translation (subluxation) in full PIP joint extension. We recorded the angle at which subluxation, if present, occurred during each testing scenario. RESULTS: Average dorsal displacement of the middle phalanx in relation to the proximal phalanx was 0.01 mm for the hemi-hamate reconstructed joints and -0.03 mm for the volar plate arthroplasty, compared with the intact state. Flexion contractures were noted in each of the specimens reconstructed with volar plate arthroplasty. Degree of contracture was directly correlated with defect size, averaging 20° for 40% defects, 35° for 60% defects, and 60° for 80% defects. We observed no flexion contractures in the hemi-hamate reconstructions. CONCLUSIONS: Surgeons can use both hemi-hamate and volar plate arthroplasty to restore PIP joint stability following a fracture dislocation with a large middle phalanx palmar base defect. Use of volar plate arthroplasty led to an increasing flexion contracture as the middle phalanx palmar base defect increased. CLINICAL RELEVANCE: Clinicians can use the information from this study to help with surgical decision-making and patient education.

Two versus 3 lag screws for fixation of long oblique proximal phalanx fractures of the fingers: a cadaver study.

PURPOSE: To compare 2- versus 3-screw fixation for oblique fractures of the proximal phalanx in a cadaver model that simulates active finger motion. METHODS: We experimentally cut the proximal phalanges of the index, middle, and ring fingers of 9 cadaveric hands. Five fingers were assigned to a control group with no fixation, and 22 were fixed with either 2 or 3 lag screws. One digit was excluded because of iatrogenic fracture during preparation. The fingers were fitted with a differential variable reluctance transducer that measured maximum interfragment displacement while the fingers were subjected to 2,000 full flexion and extension cycles to simulate a 6-week active motion protocol. RESULTS: Analysis of variance revealed a significant difference between the control group and both the 2- and the 3-screw group. The 2- and 3-screw group average displacements were not significantly different. Both of these groups were equivalent with a power of 90%. CONCLUSIONS: Biomechanical stability during simulated active motion protocol did not differ in simulated proximal phalanx fractures treated with 2 lag screws or 3. CLINICAL RELEVANCE: Fracture fixation using 2 screws may be more cost and time effective and, therefore, more attractive to the surgeon, even when 3 screws can be placed. Furthermore, surgeons may consider using 2 screws rather than resorting to plate fixation when 3-screw fixation is not possible for these types of fractures.

Evaluation of a collagen-coated, resorbable fiber scaffold loaded with a peptide basic fibroblast growth factor mimetic in a sheep model of rotator cuff repair.

BACKGROUND: A new scaffold design combined with a peptide growth factor was tested prospectively for safety and for improved tendon healing in sheep. METHODS: The infraspinatus tendon was detached and then surgically repaired to the humerus using sutures and anchors in 50 adult sheep. The repairs in 40 of these sheep were reinforced with a scaffold containing F2A, a peptide mimetic of basic fibroblast growth factor. The sheep were examined after 8 or 26 weeks with magnetic resonance imaging, full necropsy, and histopathologic analysis. A second cohort of 30 sheep underwent surgical repair--20 with scaffolds containing F2A. The 30 shoulders were tested mechanically after 8 weeks. RESULTS: The scaffold and F2A showed no toxicity. Scaffold-repaired tendons were 31% thicker than surgically repaired controls (P = .037) at 8 weeks. There was more new bone formed at the tendon footprint in sheep treated with F2A. Surgically repaired tendons delaminated from the humerus across 14% of the footprint area. The extent of delamination decreased to 1.3% with increasing doses of F2A (P = .004). More of the repair tissue at the footprint was tendon-like in the peptide-treated sheep. On mechanical testing, only 7 shoulders tore at the repair site. The repairs in the other 23 shoulders were already stronger than the midsubstance tendon at 8 weeks. CONCLUSIONS: The new scaffold and peptide safely improved tendon healing.

Torsional stability of the femur after harvest of the medial femoral condyle corticocancellous flap.

BACKGROUND: Increasingly large segments of medial femoral condyle (MFC) corticocancellous flaps have been harvested for transfer. Biomechanical evaluations demonstrated no osseous stability impairment under axial loading regardless of flap size harvested. The purpose of this study was to determine the donor site's response to torsional forces. METHODS: Dual-energy X-ray absorptiometry (DEXA) scanning was performed on 16 pairs of cadaver legs followed by removal of all soft tissues, except knee capsule and ligaments. Specimens were randomly assigned to three groups with bone harvest defects measuring 3, 5, or 7 cm in length and a control group with no osseous resection. Torsional load was applied until fracture or ligamentous failure. RESULTS: Bone failure rates were 12.5, 12.5, 28.6, and 55.6% for control, 3, 5, and 7 cm groups, respectively. Bone failure rate increased with increasing harvest size; the 7 cm group demonstrated a significantly higher rate compared with the other groups combined (55.6 vs. 17.4%; p = 0.03). Failure torque was 45.5, 29.35, 27.4, and 30.83 Nm for the control, 3, 5, and 7 cm groups, respectively (p = 0.11). Harvest of any size segment resulted in a significant decrease in failure torque (p = 0.01). Bone mineral density (BMD) and Z-scores were no different among groups (p = 0.79 and 0.59, respectively). A direct relationship was identified between force required for failure and BMD (p = 0.02) and Z-scores (p = 0.05) but not for failure location and BMD (p = 0.09) or Z-scores (p = 0.94). CONCLUSION: MFC corticocancellous flap harvest of any size decreases donor site failure torque. Flap harvests > 7 cm demonstrate a higher frequency of iatrogenic fracture and therefore warrant caution with torsional loading of the knee postoperatively. Routine preoperative DEXA scans may not be warranted.

Stability of acute dorsal fracture dislocations of the proximal interphalangeal joint: a biomechanical study.

PURPOSE: We performed a cadaveric biomechanical study to characterize proximal interphalangeal joint stability after an injury to different amounts of the volar articular base of the middle phalanx (intact, 20%, 40%, 60%, and 80% volar defects). METHODS: Eighteen digits on 6 hands were tested through full proximal interphalangeal joint range of motion using computer-controlled flexion and extension via the digital tendons. We collected proximal interphalangeal joint kinematic cine data in a true lateral projection with mini-fluoroscopy. We measured the amount of dorsal middle phalanx translation in full proximal interphalangeal joint extension. As we cycled the joint from full flexion into extension, we recorded the angle at which subluxation occurred. RESULTS: No specimens with 20% volar bony defect subluxated. All specimens in the 60% and 80% groups subluxated at an average flexion angle of 67° (range, 10° to 90°) in the 60% group and at all degrees of flexion in the 80% group. In the 40% group, 28% of specimens demonstrated subluxation at an average flexion angle of 14° (range, 4° to 40°). Mean dorsal translation of the middle phalanx in relation to the proximal phalanx at full digital extension was 0.2 mm in the 20% group, 0.8 mm in the 40% group, 3.2 mm in the 60% group, and 3.1 mm in the 80% group. CONCLUSIONS: Simulated volar articular bony defects of 20% were stable, whereas those with 60% and 80% defects were unstable during digital motion. Stability in the 40% group was variable and appeared to be the threshold for stability. CLINICAL RELEVANCE: Knowledge of the typical amount of middle phalanx defect and degree of proximal interphalangeal joint extension that can lead to joint instability may improve management of mechanically important proximal interphalangeal joint fracture dislocations.

The effect of distal radius translation in the coronal plane on forearm rotation: a cadaveric study of distal radius fractures.

PURPOSE: To determine the effect of lateral translation of the distal radius in the coronal plane on forearm rotation after distal radius fracture. METHODS: Ten fresh cadaveric limbs underwent distal radius osteotomy just proximal to the distal radial-ulnar joint to simulate an extra-articular distal radius fracture. We used an Agee Wrist Jack external fixator to create increasing magnitudes of distal fragment lateral translation in 2-mm increments. Forearm rotation was measured using a 3-dimensional camera at each magnitude of lateral translation. RESULTS: Total forearm rotation for the intact specimen and 2, 4, 6, and 8 mm (maximal) radial translations was 186° ± 53°, 188° ± 54°, 189° ± 55°, 190° ± 57°, and 193° ± 59°, respectively. There was no significant difference for any magnitude of radial translation. The average maximal radial translation possible before radioulnar abutment was 8 ± 0.5 mm. CONCLUSIONS: In this cadaveric model, translation of the distal radius fragment in the lateral direction had no effect on forearm rotation. CLINICAL RELEVANCE: At the level of the proximal border of the distal radioulnar joint, isolated distal radius translation does not significantly affect forearm rotation.

The biomechanical stability of salvage procedures for distal radioulnar joint arthritis.

PURPOSE: To test distal forearm stability after 3 surgical procedures for distal radioulnar joint (DRUJ) arthritis. METHODS: We tested 11 cadaver limbs with the DRUJ intact, after distal ulna-matched hemiresection, after Darrach distal ulna resection, and after unlinked total DRUJ arthroplasty. We evaluated distal forearm stability in neutral rotation, full pronation, and full supination in unweighted and 1-kg-weighted conditions. We measured dorsal/palmar translation and convergence/divergence of the distal radius relative to the ulna. RESULTS: Under neutral rotation, whether weighted or unweighted, matched hemiresection and Darrach specimens demonstrated significant radioulnar convergence relative to intact specimens. Weighted and unweighted, DRUJ arthroplasty demonstrated similar radioulnar convergence to intact. Weighted and unweighted, only Darrach specimens showed significant radius-palmar translation compared with intact, hemiresected, and DRUJ arthroplasty. In pronation, no testing scenario, either weighted or unweighted, demonstrated statistically significant radioulnar convergence relative to intact state. In unweighted pronation, palmar translation of the radius was significantly different from the intact state for all surgical scenarios and the Darrach was significantly worse than the other procedures. In weighted pronation, palmar translation of the radius was significantly different from the intact state for all surgical scenarios and the matched hemiresection was significantly better than the other procedures. In supination, weighted and unweighted, Darrach specimens had significant radioulnar convergence relative to intact. Either weighted or unweighted, the hemiresection and arthroplasty groups demonstrated similar radioulnar convergence relative to intact. Unweighted, all scenarios demonstrated similar dorsal translation of the radius. Weighted, the Darrach group showed significant radius-dorsal translation relative to intact specimens. CONCLUSIONS: For tested procedures, DRUJ arthroplasty overall was biomechanically superior to the other conditions except that we found greater stability in the hemiresected group in weighted pronation. CLINICAL RELEVANCE: Knowledge of baseline biomechanical characteristics of DRUJ arthritis procedures will aid surgical decision-making and patient counseling.